Hello. Quick question about Residential Networks: how can I test the bandwidth my network is using?

Background: I am finally breaking free from my cable ISP rental equipment, and I think I am massively overbuying service. I understand speed, and I can test speed until my hair falls out. But, I also want to test bandwidth-used so I can reassess my service needs. I have had the Deco 70 Pro devices (3) in place for 5 days. So far, the speeds throughout our home have significantly increased with the new Deco mesh. I am not a power user or IT professional, so something easy would be ideal. Thanks for your consideration.